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A nonreciprocal polarization converter compatible with InP-based photonic integrated circuits is described, where the device consists of an asymmetric InGaAsP waveguide combined with a ferromagnetic cerium-substituted yttrium iron garnet layer. The nonreciprocal conversion of the polarization state is used in the waveguide and a nonreciprocal TE-TM conversion efficiency of 93% is obtained with a device length of 0.27 nm.

Hybrid spintronic structures, integrating half-metallic magnetic oxides and Heusler alloys with their predicted high spin polarization, are important for the development of second-generation spintronics with high-efficient spin injection. We have synthesized epitaxial magnetic oxide [Fe.sub.3][O.sub.4] on GaAs(100) and the unit cell of the [Fe.sub.3][O.sub.4] was found to be rotated by 45[degrees] to match the gallium arsenide GaAs. The films were found to have a bulk-like moment down to 3-4 nm and a low coercivity indicating a high-quality magnetic interface. The magnetization hysteresis loops of the ultrathin films are controlled by uniaxial magnetic anisotropy. The dynamic response of the sample shows a heavily damped precessional response to the applied field pulses. In the Heusler alloy system of [Co.sub.2] MnGa on GaAs, we found that the magnetic moment was reduced for thicknesses down to 10 nm, which may account for the lower than expected spin-injection efficiency from the spin-light-emitting diode structures. Using the element-specific technique of X-ray magnetic circular dichroism (XMCD), the reduced spin moments were found to originate from the Mn rather than the Co atoms, and the improvement of the interface is thus needed to increase the spin injection efficiency in this system. Further studies of the I--Vcharacteristics of [Fe.sub.3][O.sub.4]/GaAs(100) and [Fe.sub.3][O.sub.4]MgO/GaAs(100) show that the [Fe.sub.3][O.sub.4]-based spintronic structures have a well-defined Schottky or tunneling barrier of moderate barrier height, which is encouraging for high-efficient spin injection. Index Terms--Gallium arsenide (GaAs), Heusler alloys, magnetic oxides, magnetite, molecular-beam epitaxy, spintronics, ultra-thin films.

The electronic properties of delta-doped In0.22Ga0.78As/GaAs quantum wells (QWs) are studied by van der Pauw Hall measurements and Shubnikov-de Haas measurements. From the temperature-dependent van der Pauw Hall measurements, two kinds of donors are observed, which have binding energies of 104 (plusmn) 7 and 9.6 (plusmn) 0.1 MeV.

Temperature-dependent (2 to 300K) magnetic susceptibility measurements of undoped GaAs substrate is described. It is shown that in the entire temperature range from 2 to 300K the functional behavior of magnetic susceptibility of GaAs follows the temperature dependence of the band gap.

The effect of the V/III flux ratio and substrate temperature on magnetotransport properties and lattice parameters of Ga0.96Mn0.04As grown by molecular-beam epitaxy (MBE) are investigated. The results suggest that the lattice parameter of Ga0.96Mn0.04As increased with decreasing V/III ratio and increasing growth temperature.

A study is carried out on the magnetic and transport properties of insulating and metallic (Ga,Mn)As layers before and after annealing. The results show a dramatic increase of the ferromagnetic transition temperature Tc by post growth annealing that is realized in both insulating and metallic (Ga,Mn)As.

An investigation was conducted on the magnetotransport properties of ferromagnetic Ga(sub 1-x)Mn(sub x)As epilayers with Mn mole fractions in the range of x approximately 2.2%-4.4% by using Hall effect measurements. The results of the magnetoresistance measurements confirms that the anomalous Hall effect existed in Ga(sub 1-x)Mn(sub x) samples that showed metallic and insulating behavior, respectively.

A research was carried out on the influence of sub-micrometer geometric constrictions on 90 degree magnetic domain-wall nucleation and propagation in stripes of ferromagnetic (Ga0.95,Mn0.05)As. The results show that the demagnetizing fields are found to play a crucial role in the switching behavior around the region of the constriction.

The perpendicular magnetic properties of CoCr films on GaAs substrates are investigated by magneto-optical Kerr-effect measurements. The direct deposition of the CoCr film on the GaAs substrate did not show any perpendicular properties and the thickness dependence of the hysteresis loop and the magnetic force microscopy showed that the onset thickness of ferromagnetism was 6.5nm.

A detailed analysis of the structural and magnetic properties of as-grown MnAs films deposited on (001)- and (113) A-oriented GaAs substrates is prepared. The stripe pattern, representing an array of micromagnets, changes in a characteristic manner with the film thickness.

Pseudomorphic Ni2MnGa and Ni2Mn(sub 1.2)Ga(sub 0.8) films were grown by molecular-beam epitaxy on GaAs substrates using a six monolayer thick interlayer. Removal of the substrates to release the films enables martensitic phase transformation in the free-standing single crystal films to occur.

The Fe/Cr/Fe trilayers are epitaxially grown on atomically flat GaAs(001). The superconducting quantum interference device measurements confirm the interpretation of the magneto-optical Kerr effect (MOKE) loops and demonstrate homogeneity and sharpness of the interfaces in the structures.

GaAs thin films with embedded Mn(Ga)As magnetic nanoclusters have been synthesized by annealing (Ga, Mn)As diluted material grown by low-temperature molecular-beam epitaxy (MBE). Strong ferromagnetic behavior is observed only in films with hexagonal clusters.

The fabrication of nanoscale zinc-blende MnAs dots on the sulfur-passivated GaAs (001) substrates is examined. Results indicate the localization of Mn 3d electrons in the nanoscale zinc-blende MnAs dots due to the many-body effect.

The enhanced positive magnetoresistance effect was observed in GaAs containing nanoscale magnetic clusters. Positive magnetoresistance in these structures was observed and attributed to the enhanced geometric magnetoresistance effect in inhomogeneous semiconductors with metallic inclusions.

The growth of Fe by molecular beam epitaxy (MBE) on GaAs (110), (311)A, and (331)A substrates to obtain macroscopically smooth layers is studied. Less As-rich surface reconstructions produce macroscopic defects whose density increases on more Ga-rich surface reconstructions.

Amorphous and crystalline thin films of Mn-doped (0.5%-10%) GaAs and crystalline thin films of [Zn.sub.1-x][Co.sub.x]O(x = 3%-20%) were investigated by means of magnetic susceptibility and electron spin resonance (ESR). For the Mn-doped GaAs samples, our results show the absence of ferromagnetic ordering for the amorphous films in the 300 > T > 2 K temperature range, in contrast to the ferromagnetism found in crystalline films for [T.sub.c] < 110 K. A single ESR line with a temperature independent g-value (g ~ 2) is observed for the amorphous films, and the behavior of this ESR linewidth depends on the level of crystallinity of the film. For the Mn-doped GaAs crystalline films, only a ferromagnetic mode is observed for T < [T.sub.c] when the film is ferromagnetic. Turning now the [Zn.sub.1-x][Co.sub.x]O films, ferromagnetic loops were observed at room temperature for these films. The magnetization data show an increasing of the saturation magnetization [M.sub.s] as a function of x reaching a maximum value for x [approximately equal to] 10%. ESR experiments at T = 300 K in the same films show a strong anisotropic ferromagnetic mode (FMR) for x = 0.10. Index Terms--Dilute ferromagnetic semiconductors, electron spin resonance, magnetization curves.

Holographic transmission electron microscopy showed that magnetic flux does not diverge from the top of an Fe-coated W tip indicating the in-plane magnetization at the apex of successful spin-polarized tips. A dependence of differential conductivities of GaAs with Fe-coated W tips on the helicity of illuminating laser light was confirmed at negative sample bias where partially spin-polarized electrons in the conduction band of p-GaAs tunnel into spin-dependent Fe empty states while no dependence of those with nonmagnetic W tips. Index Terms--Magnetic field measurement, optical pumping, spectroscopy, tunneling.

Magnetically tunable wideband microwave bandstop and bandpass filters using ferromagnetic resonance absorption in yttrium iron garnet/gadolinium gallium garnet-gallium arsenide (YIG/GGG-GaAs) layer structures are reported. The measured characteristics of the bandstop filter, with nonuniform bias magnetic field distribution along the YIG/GGG film, shows a large absorption bandwidth of 1900 MHz at the stopband center frequency of 11.0 GHz, average peak absorption of 13 dB, and an out-of-stopband insertion loss of 1.5 dB. The measured characteristics of the bandpass filter at the passband center frequency of 7.1 GHz demonstrates a 3-dB bandwidth of 1450 MHz, out-of-band rejection of 33 dB, and an insertion loss of 1.5 dB. A good agreement between the experimental results and the simulation results based on a lumped element equivalent circuit modeling of YIG bandstop filters has been achieved. Index Terms--Ferromagnetic resonance (FMR) absorption, tunable bandstop and bandpass filters, YIG filters.

We report the evolution of Fe oxide nanostructures on GaAs(100) upon pre- and post-growth annealing conditions. GaAs nanoscale pyramids were formed on the GaAs surface due to wet etching and thermal annealing. An 8.0-nm epitaxial Fe film was grown, oxidized, and annealed using a gradient temperature method. During the process the nanostripes were formed, and the evolution has been demonstrated using transmission and reflection high energy electron diffraction, and scanning electron microscopy. These nanostripes exhibited uniaxial magnetic anisotropy. The formation of these nanostructures is attributed to surface anisotropy, which in addition could explain the observed uniaxial magnetic anisotropy. Index Terms--Annealing, magnetic Fe oxide, magnetic uniaxial anisotropy, nanostructures.

The magnetic moments of ultrathin Fe films on three different III-V semiconductor substrates, namely GaAs, InAs and [In.sub.0.2][Ga.sub.0.8] As have been measured with X-ray magnetic circular dichroism at room temperature to assess their relative merits as combinations suitable for next-generation spintronic devices. The results revealed rather similar spin moments and orbital moments for the three systems, suggesting the relationship between film and semiconductor lattice parameters to be less critical to magnetic moments than magnetic anisotropy. Index Terms--Fe/InGaAs, interface magnetism, spin electronics, ultrathin films.

Ultrathin Fe oxide films of various thicknesses prepared by post-growth oxidation on GaAs(100) surface have been investigated with X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), and X-ray magnetic circular dichroism (XMCD). The XPS confirms that the surfaces of the oxide are [Fe.sub.3][O.sub.4] rather than [Fe.sub.2][O.sub.3]. XAS and XMCD measurements indicate the presence of insulating Fe divalent oxide phases (FeO) beneath the surface [Fe.sub.3][O.sub.4] layer with the sample thickness above 4 nm. This FeO might act as a barrier for the spin injection into the GaAs. Index Terms--Half-metallic [Fe.sub.3][O.sub.4], post-growth oxidation, spintronics, XMCD.

A low transmission barrier is a crucial factor for the efficient spin injection, and an oxide barrier is commonly used for the insulator between the ferromagnet and the semiconductor. After heat treatment at the furnace, an AlAs layer was converted to an aluminum oxide layer, and arsenic gas was evaporated. This new method of forming spin injection barrier on the two-dimensional electron gas (2-DEG) system is very efficient to obtain tunneling behavior. Index Terms--A1As, aluminum oxide, furnace, low transmission barrier, spin injection.

The electron beam induced switching of the magnetic state of epitaxial single-crystal Fe(110) films grown on atomically flat cleaved GaAs(110) was observed using scanning electron microscopy with polarization analysis. The electron beam permanently reduces the strength of the pinning sites without permanently affecting the overall magnetocrystalline anisotropy that creates the metastable and stable configurations.

The phase diagrams for magnetic reversal in bcc Fe(sub 1-x)Co(sub x) on vicinal Sc(sub 1-y)Er(sub y)As/GaAs(100) are explored by tuning the relative strength of the uniaxial anisotropy. The first jump in the reversal process occurs at positive magnetic fields, when the anisotropy has a local maximum, and as the angle between the in-plane magnetic field and the hard axis increases, this jump crosses over to continuous rotation.

Magneto-optic Kerr effect was used for examining the magnetic properties of the epitaxial Fe(sub 1-x)Co(sub x) alloy films grown on GaAs(001). Ferromagnetic order at room temperature for thickness above 4 ML was observed.

The connection between the onset of ferromagnetism with an onset of magnetic anisotropy is examined. Ferromagnetic long-range order and uniaxial magnetic anisotropy appear for T >0 above a critical thickness of 2.5 ML suggesting the strong correlation between the onset of ferromagnetism and of magnetic anisotropy for Fe on GaAs(001).

The relation between the strong uniaxial magnetic anisotropy of Fe/GaAs(001) with the specific GaAs(001) surface reconstruction is examined. The easy axis of the uniaxial anisotropy is found along [110] in Fe(001) films grown by molecular-beam epitaxy on Ga-rich GaAs(001) surfaces at room temperature.

The magnetic relaxation in epitaxial Fe(sub 1-x)Co(sub x) films grown on vicinal GaAs (100) surfaces is examined with the help of time-resolved ferromagnetic resonance. The decay time for the envelope of the z component of magnetization is 25 percent shorter for disks for a given set of anisotropy parameters and damping constants.

The magnetic properties of nanopatterned epitaxial iron films on GaAs are discussed. A strong dependence of their remanent state of the Fe(110) elements was observed on the magnetic history whereas Fe(001) elements displayed the same remanent magnetization pattern.

The technique for fabrication of planar Hall sensors from GaAs-AlGaAs heterojunctions used for examining the local stray field at a specific section of a micron-sized magnet is described. The occurrence of the magnetization reversal via a magnetic vortex structure was suggested by the hysteresis loop of an electroplated Ni ring measured at 110 K.

The epitaxial growth of zinc-blende CrAs/GaAs multilayer with thick zinc blende-CrAs layer in total is examined. CrAs and GaAs do not grown epitaxially when the thickness of CrAs layer is greater than 2 ML and the thickness of GaAs layer is smaller than 2 ML.

The preparation of p-(In,Mn)As/n-InAs/p-(In,Mn)As trilayer structures by molecular beam epitaxy on GaSb/GaAs/GaAs (001) substrates is examined. Ferromagnetic coupling of the magnitude J = 7.6 * 10(super -3) mJ/m(super 2) is observed between the two magnetic p-(In,Mn)As layers with a thick n-InAs layer.

The electronic structures and magnetic properties of GaAs-based ferromagnetic semiconductor with a high Cr content, (Ga, Cr)As are discussed. A flat surface is observed in (Ga, Cr)As thin film up to the Cr content of 0.18 whereas larger roughness of the film is observed when the Cr content exceeds 0.20.

The structure and magnetism of Co(sub 1-x)Mn(sub x) films grown on GaAs(001) substrates were characterized by reflection high-energy electron diffraction and magneto-optical Kerr effect measurements. The co-rich and Mn-rich films exist in body-centered-cubic and face-centered-cubic structures respectively.

Single crystal Co(sub 2) MnGe Heusler alloy films were epitaxially grown on GaAs substrates by molecular beam epitaxy. Ferromagnetic resonance of these ordered alloy films show narrow linewidths and a small anisotropy.

The article presents a comparative study of the different methodologies that can be employed for determining the trap densities observed at the high-permittivity (k) dielectric/III-V semiconductor interfaces. The conductance method, Berglund integral and Terman methods are shown to be some of the main methods employed for the purpose.

The distribution of coexisting structural domains exhibited in the MnAs layers grown on the GaAs substrates is analyzed. The inhomogeneity observed in the magnetic, as well as the electrical properties of the layer is also studied.

The electrons effective masses in double barrier resonant tunneling diodes prepared on the InGaAs/GaAsSb material system are examined by using magnetotunneling experiments. The studies have shown that due to the nonparabolic band structure in the material system, the electron effective masses have increased on samples with smaller well width and higher resonance energies.

The planar Hall effect is employed to explain the various effects of uniaxial anisotropy on the domain pinning fields of the different ferromagnetic [La.sub.0.8][Ca.sub.0.2]Co[O.sub.3] nanoparticles. The values of the pinning fields is shown to be highly dependent on the direction of the magnetic easy axis.

First-principles calculations are used for studying the interlayer exchange coupling (IEC) in a series of model diluted magnetic semiconductor multilayers consisting of two magnetic (Ga, Mn)As layers separated by nondoped or Be-doped GaAs nonmagnetic spacers. The studies have shown that for the Be-doped GaAs spacers, the IEC is tunable and the antiferromagnetic IEC is achieved via Be-doping in the interfaces between the (Ga, Mn)As layers and the spacers.

Several studies are conducted to explain the different phase-breaking effects taking place in the double-barrier resonant tunneling diodes exhibiting different spin-orbit interactions. The magnitude of the spin polarization taking place in the system is shown to be highly dependent on the quasibound state broadening.

The magnetooptical Kerr effect is employed to explain the different shapes exhibited by the hysteresis loops of the GaMnAs thin films grown on different substrates. The linear dependence of the magnetooptical effects on the magnetization components is shown to be extremely helpful in determining the impact of the changing magnetic field on the orientation of magnetization in the loops.

Electrical spin-injection across the [Fe.sub.3][O.sub.4]:[Al.sub.0.1][Ga.sub.0.9]As interface is measured. The studies have shown the first step in the integration of molecular beam epitaxy-grown magnetic oxides into III-V semiconductor devices.

Several studies are conducted to explain the magnetic properties observed in the planar structure that consists of ferromagnetic metal, magnetic semiconductor, as well as a quantum well. The high-temperature spin polarization of the high-mobility charge carriers observed in these structures is also analyzed.